Tensions between the US and Iran have been escalating in recent days.
Here's a look at the most recent developments in the two nations' relationships:
There is no indication the United States has been talking to Iran, even through a backchannel, a senior diplomatic source from a US ally told CNN.
The source was also critical of US tactics regarding Iran leading up to the latest incident involving the shootdown of a US drone.
While Washington says the goal is to re-establish deterrence on Iran, the source said “re-establishment of deterrence is escalation. US actions brought us where we are today. Yet, meanwhile, the Iranians keep hearing Trump saying he doesn’t want war. So they’ll keep going right up to what they feel is the current line."
President Trump described in more detail his decision to pull back strikes on Iran, saying he didn't feel an attack that left 150 dead was proportionate to the downing of a US drone.
"Nothing was greenlighted until the very end because things change," Trump said in an interview with NBC News. "We had something ready to go subject to my approval."
Trump said planes were not in the air when he ordered the pull back, but "would have been pretty soon."
"Things would have happened to a point where you would not turn back, you could not turn back," he said.
Trump said he asked his national security officials how many would be killed if he went forward, and was given an approximate figure of 150.
"I thought about it for a second and I said, you know what, they shot down an unmanned drone, plane, whatever you want to call it, and here we are sitting with a 150 dead people that would have taken place probably within a half an hour after I said go ahead, and I didn’t like it, I didn’t think, I didn’t think it was proportionate," Trump said.
The source said key players in the decision were not all huddled in the Situation Room. Some White House officials involved weren't physically in the White House and Department of Defense officials were at the Pentagon.
The source said while President Trump had received the risk assessment before the strike, "he made the call when he internalized the severity of casualties."
Once they had almost reached the trigger point, the President made the final call.
There was unanimity on the strike, led by national security adviser Bolton. Vice President Mike Pence and Secretary of State Mike Pompeo were also in agreement. Other officials agreed that there needed to be some kind of response. The source made clear that officials still believe a response is needed and that is what they are considering today. There were different responses presented and different voices about whether the strike was the right response.
There was a P-8 surveillance aircraft operating in the area at the time Iran shot down a RQ-4 yesterday, a US official tells CNN.
The plane was in international airspace, the official said.
According to the US Navy, the P-8 aircraft is configured to carry a crew of 9 people.
"While we were tracking the spy drone there was also a P-8 spy plane with 35 crew on board which we could have shot at, but we did not do so," Hajizadeh said.
President Trump is tweeting about his decision to stop an operation to strike Iran last night.
"We were cocked & loaded to retaliate last night on 3 different sights when I asked, how many will die," he tweeted. "150 people, sir, was the answer from a General. 10 minutes before the strike I stopped it, not proportionate to shooting down an unmanned drone."
Tensions have been escalating between the US and Iran. If you're just getting caught up, here's what you need to know: